i just read this topic http://arduino.cc/forum/index.php/topic,10437.0.html and i learn a bit about SSR with zero cross trigger as control method. Well here is the question i want control a water-pump ( 13A, 60Hz , 1HP,... ) and 2 exractors ( each 6.6 A ) from this http://www.fotek.com.tw/pdf/etc_33.pdf i chose a SSR-25DA model, but i am just 95% sure about buy this, and i want be 100%. Can u tell me if i can control turn on/off the water-pump and the extractos with 2 SSR-25DA when i want from my arduino MEGA??? and what about this zero cross trigger method how many dealy will cause?? i read this method is for protection.

By "no guarantee" I mean I have given you my opinion only. As writers on this forum we only give opinions - most, hopefully, are technically correct but occasionally some are incorrect.

The device operates at zero cross-over point. In any full cycle there are 2 cross-overs, 0 degrees and 180 degrees. Assuming your trigger has just missed a cross-over, the turn-on will not occur until the next one, which will be just under one-half cycle into the future. At 60Hz the period is 1/60seconds = 16.666 mS, so 1/2 cycle period is 8.333 mS. Hence, if you just miss a cross-over point, the next one will be a maximum of 8.333 mS away (ie the delay time)

Inductive loads such as motors and probably your pump should be controlled by random-fire SSRs, not zero-crossing ones. A zero-crossing SSR feeding an inductive load will turn off prematurely part way through each half cycle of power.

Formal verification of safety-critical software, software development, and electronic design and prototyping. See http://www.eschertech.com. Please do not ask for unpaid help via PM, use the forum.